This invention is directed to a multi-element, adjustable structural header beam that is adapted to be used in existing construction, such as in the building of a residential house, office building or in other similar building structure. It is also particularly usable where it is desired to reinforce existing floor or ceiling joists and/or to replace existing header beam(s) in order to remove one or more existing decayed or broken header or section of a header. It is further useful for inserting functional elements, such as a drain or water pipe, or a toilet and associated drain pipe configurations in a floor defined by the header. The header of this invention is conveniently made of conventional structural building materials, such as steel.